You'll get a lot of debate over that one. Every era has its usual suspects.
The 60's? St. Raphael (Anquetil/ Stablinski/ Darrigade/ Saint/ Riviere/Elliott)? Peugeot (Simpson/Merckx/Pingeon/Bracke)? Flandria (Van Looy/Godefroot/Janssen/Zietemelk/Leman/De Vlaeminck)?
70's? How 'bout Molteni (Eddy Merckx/Bruyere/Swerts)? Mercier (Poulidor)? Kas? Bianchi?
The 80's? The Dutch TI Raleigh squad (Raas, Knetemann, Zoetemelk)? Renault-Gitane (Hinault/Fignon/LeMond/ Madiot)? Or maybe LaVie Claire (Hinault/ Lemond/Bauer)?
90's? Had to be Mapei (Rominger/Museeuw/Tafi/VDB/Ballerini) or was it Miguel Indurain's Banesto? The past decade that saw Lance's US Postal juggernaut morph into Discovery and then Astana? Or CSC/Saxo Bank?
Your opinion counts, so take the poll!